Thermostatically controlled electric circuit



y 1932- A c BURLEIGH 1,859,765

THERMOSTATICALLY CONTROLLED ELECTRIC CIRCUIT I Filed Aug. 16, 1928 lnvenTorQ Aflhur C. Bufleigh b WM W ATTya Patented May 24, 1932 UNITED STATES PATENT OFFICE I THERMOSTATICALLY CONTROLLED ELECTRIC CIRCUIT Application filed August 16, 1928. Serial No. 300,083.

This inventinon relates to a thermostatically controlled electric circuit, and it has for one of its objects to provide a novel construction by which the current flow in the circuit will be automatically varied depending upon variations in temperature. In carrying out my invention I employ a pressure rheostat for controlling the current in the circuit, and I provide means responsive to temperature changes to vary the pressure of the pressure rheostat and thereby vary the resistance in the circuit.

My invention is adapted for wide variety of uses and it may be so constructed that an increase of temperature will decrease the pressure of the pressure rheostat and thereby increase the resistance in the circuit, while a decrease of temperature will increase the pressure of the pressure rheostat and thereby decrease the resistance, or it may be so constructed that it will act in the reverse manner, that is, so that an increase of temperature will increase the pressure of the pressure rheostat and thereby decrease the resistance in the circuit, while a decrease of temperature will decrease the pressure of the pressure rheostat and thereby increase the resistance in the circuit.

While, as stated above, the invention is capable of a wide variety of uses, I have chosen herein to illustrate it as it might be used in controlling a heating circuit, but I wish to state that the invention is not at all limited to use in connection with a heating circuit.

The complete device comprises a circuit which carries the current to be regulated, a pressure rheostat in the circuit, and means responsive to temperature changes for automatically varying-the pressure of the pressure rheostat and therebyvarying the resistance in the circuit.

In order to give an understanding of my invention I have illustrated in the drawings some selected embodiments thereof in which the current to be controlled is a heating current, and in the drawings.

Figure 1 is-a sectional View illustrating a simple form of thermostatic control for an electric circuit embodying my invention;

Fig. 2 is a view similar to Fig. 1, but showing a difierent embodiment of the invention.

Referring first to Fig. 1, 1 indicates an electric circuit having a source of electric supply 2 therein and also being provided with a switch 3 by which the circuit may be opened and closed.

Situated in the circuit 1 is a pressure rheostat 4 which is illustrated as comprising a plurality of blocks 5 of carbon, graphite, or any other suitable material, which are enclosed in a sleeve 6 of insulating material and are confined between two terminals 7 and 8.

Since the pressure rheostat 4 is in the circuit 1 the amount of current will depend upon the pressure in the pressure rheostat, and this in turn is controlled by means responsive to temperature rhanges In the construction herein. shown such means is in the form of a sleeve or shell 9 in which the terminals 7 and 8 are anchored at opposite ends thereof. The terminal 7 is insulated "from the shell 9 and is provided with a stem 10 which extends through a sleeve 11 of insulating material located in the shell 9 at one end thereof, the extremity of the shell being spun over at 12 to form a flange against which the sleeve 11 abuts.

The terminal 8 is shown as having a screw- 50 threaded stem 13 which is screwed into the end of the shell 9, and said stem has a binding post 14 to which one lead wire of the circuit 1 is secured, the other lead Wire being connected to the stem 10 of the terminal 7.

Since the pressure rheostat 4 is in the circuit 1 the resistance of the circuit will vary as the pressure of the pressure rheostat varies, it being understood that as the pressure increases the resistance will be correspondingly decreased, while as the pressure decreases the resistance will be correspondingly increased.

The shell 9 is of a material having a different coeflicient of expansion from that of the blocks 5 of the pressure rheostat 4:, and consequently whenever there is any change of temperature, either an increase or a decrease, the shell 9 will expand or contract to a greater or less degree than the blocks 5.

If, for instance, the shell 9 has a greater coeflicient of expansion than the blocks 5 of the pressure rheostat 4, then in case of an increase of temperature of said shell and the blocks 5, said shell will expand to a greater extent than the blocks 5 with the result that the pressure on the blocks 5 will be decreased, which, obviously, will result in increasing the resistance in the circuit.

On the other hand, if the coefficient of expansion of the shell 9 is less than that of the blocks 5, then upon an increase of temperature the blocks 5 will expand longitudinally to a greater extent than the shell 9, which will result in increasing the pressure in the pressure rheostat and thereby decrease the resistance in the circuit.

Conversely, if the shell 9 has a greater coefiicient of expansion than the blocks 5 then a decrease of temperature will cause the shell to contract to a greater extent than the blocks 5, which will result in increasing the pressure in the pressure rheostat and thereby decreasing the resistance.

On the other hand, if the coeificient of expansion of the shell 9 is less than that of the blocks 5 a decrease of temperature will cause the shell to contract less than the blocks 5, which will result in decreasing the pressure of the pressure rheostat and thereby lncrease the resistance in the circuit.

The question as to whether the shell 9 should have a greater or less coeflicient of expanion than that of the blocks 5 depends upon the use to which it is desired to put the invention. If it is desired to provide for increasing the resistance in the circuit as the temperature rises and decreasing the resistance as the temperature falls, then the shell 9 will be made of a material having a greater coeflicient of expansion than that of the blocks 5. On the other hand, if it is desired to decrease the resistance in the circuit 1 when the temperature rises, then the shell 9 will be made of a material which has a coefiicient of expansion less than that of the blocks 5.

As applied to the control of a heating circuit I will use material for the shell 9 which has a greater coeEcient of: expansion than that of the blocks 5. When the device is embodied in a heating circuit the heat may be developed directly from the pressure rheostat or may be developed from a separate coil.

The construction shown in Fig. 1 illustrates the invention as applied to a heating circuit in which the heat is developed by the pressure rheostat itself. In this embodiment the heat developed by the rheostat will heat the shell 9, the heat being taken from the shell for any desired purpose. If the heat is being developed faster than it is being drawn out from the shell so that the latter begins to increase in temperature, then the greater expansion of the shell over that of the blocks will cause a separation of the terminals 7 and 8, which will result in a decrease of-the pressure in the pressure rheostat and a consequent increase of the resistance in the circuit 1.

This increase of resistance will cut down the current and thus reduce the amount of heat being developed.

On the other hand, if the heat is being drawn from the shell 9 faster than it is being developed, there will be a decrease of temperature in the shell and pressure rheostat which will result in an increase of pressure in said rheostat with the consequent decrease of resistance in the circuit, and such decrease of resistance will cause. an increase in the current.

In Fig. 2 I have illustrated an embodiment of the invention in which the heat is developed by a heating coil which is separated from the pressure rheostat. Such heating coil is shown at 15, and it is located in the circuit 1 and may be conveniently situated so that the shell 9 may be heated therefrom. This heating coil may be used to heat any object, such, for instance, as a flatiron, curlingiron, hot plate, or, in fact, any similar object that is to be electrically heated. In installing the device the heating coil 15 will preferably be sufiiciently close to the shell 9 so that the latter will become heated from the coil 15 and will have a temperature corresponding to that of the article which is to be heated by said coil 15.

The device shown in Fig. 2 operates in the same manner as that shown in Fig. 1. An increase in the temperature of the shell 9 will cause a decrease in the pressure in the pressure rheostat and thereby an increase in the resistance in the circuit, which will result in cutting down the current, while when the temperature of the shell decreases there will be a resultant increase in the pressure of the pressure rheostat with a corresponding decrease of resistance in the circuit which will increase the current flow.

The screw 13 provides an adjustment for the terminal 8 by which an initial setting of the pressure rheostat may be secured, which setting will vary somewhat depending upon the use to which the invention is to be put.

lVhile I have above referred specifically to the use of the invention as controlling a heating circuit yet I wish to repeat what has been that the invention is stated before, that is, equally capable of use for controlling circuits designed for other purposes than heating. I also wish to state that the invention is not limited to a construction in which the heat or temperature to which the shell 9 is responsive is developed in the circuit 1, as the source of heat by which the shell 9 is heated might be entirely outside of the circuit 1 without in any way departing from the invention.

I claim v The combination with an electric circuit, of a heating coil therein and means for controlling the operation of the heating coil comprising a tubular member of heat-conducting material sitiiated adjacent the heating coil and adapted to be heated thereby and therefore expanding and contracting in response to variations in its temperature due to heat received from the heating coil, two terininals carried by said tubular member and connected in series in said circuit, one of said 6 terminals being insulated from the tubular member, a plurality of resistant blocks within the tubular member and situated between and held under pressure by the terminals, one of the terminals being adjustable toward and from the other to vary the pressure of the resistant blocks and correspondingly to vary the resistance of the circuit.

In testimony whereof, I have signed my name to this specification. 2o ARTHUR C. BURLEIGH. 

